I'd like to suggest to add the BusyBox 'stat' applet the next time BusyBox gets re-build. I can't imagine that it will increase the size of the resulting binary by much.
This suggestion was triggered when reading this
thread, as it would allow for an easier way to rename files based on their modification time. I'm aware that the GNU version of it should be available via the 'coreutils.tcz' extension, but I could envisage it's use also in the Core.